The Society of Automotive Engineers (SAE) has defined multiple levels of autonomous vehicle operation. At levels 0-2, a human driver monitors or controls the majority of the driving tasks, often with no help from the vehicle. At level 0 (“no automation”), a human driver is responsible for all vehicle operations. At level 1 (“driver assistance”), the vehicle sometimes assists with steering, acceleration, or braking, but the driver is still responsible for the vast majority of the vehicle control. At level 2 (“partial automation”), the vehicle can control steering, acceleration, and braking under certain circumstances without human interaction. At levels 3-5, the vehicle assumes more driving-related tasks. At level 3 (“conditional automation”), the vehicle can handle steering, acceleration, and braking under certain circumstances, as well as monitoring of the driving environment. Level 3 requires the driver to intervene occasionally, however. At level 4 (“high automation”), the vehicle can handle the same tasks as at level 3 but without relying on the driver to intervene in certain driving modes. At level 5 (“full automation”), the vehicle can handle almost all tasks without any driver intervention.
During Level 2 or 3 autonomous driving, a vehicle occupant is expected to maintain attention on the task of driving the vehicle while the vehicle performs many of the actions of the driving task and/or be prepared to take over operation of the vehicle. During Level 4 autonomous driving, the vehicle may request that the driver intervene when entering particular environments, and during Level 5 autonomous driving, the driver may still request to take control of the vehicle. Handing over control from the vehicle to the driver is a problem in semi-autonomous and autonomous vehicles that allow manual driving. If the vehicle is nonautonomous or operating nonautonomously, then the handover process does not arise because the driver entirely or mostly maintains control of the vehicle.